Glucocorticoid receptor β and histone deacetylase 1 and 2 expression in the airways of severe asthma

Rationale Upregulation of glucocorticoid receptor beta (GR beta) has been implicated in steroid resistance in severe asthma, although previous studies are conflicting. GR beta has been proposed as a dominant negative isoform of glucocorticoid receptor alpha (GR alpha) but it has also been suggested that GRb can cause steroid resistance via reduced expression of histone deacetylase 2 (HDAC2), a key regulator of steroid responsiveness in the airway. Objectives To examine GR beta, GR alpha, HDAC1 and HDAC2 expression at transcript and protein levels in bronchial biopsies from a large series of patients with severe asthma, and to compare the findings with those of patients with mild to moderate asthma and healthy volunteers. Methods Bronchoscopic study in two UK centres with real-time PCR and immunohistochemistry performed on biopsies, western blotting of bronchial epithelial cells and immunoprecipitation with anti-GR beta antibody. Measurements and main results Protein and mRNA expression for GR alpha and HDAC2 did not differ between groups. GR beta mRNA was detected in only 13 of 73 samples (seven patients with severe asthma), however immunohistochemistry showed widespread epithelial staining in all groups. Western blotting of bronchial epithelial cells with GR beta antibody detected an additional 'cross-reacting' protein, identified as clathrin. HDAC1 expression was increased in patients with severe asthma compared with healthy volunteers. Conclusions GR beta mRNA is expressed at low levels in a minority of patients with severe asthma. HDAC1 and HDAC2 expression was not downregulated in severe asthma. These data do not support upregulated GRb and resultant reduced HDAC expression as the principal mechanism of steroid resistance in severe asthma. Conflicting GR beta literature may be explained in part by clathrin cross-reactivity with commercial antibodies.